1. Field of the Invention
This invention relates generally to a power supply for vibrating compressors, and more particularly to a power supply for vibrating compressors adapted to generate an a-c voltage of a frequency following the resonance frequency (natural frequency) of the vibrating compressor, which tends to fluctuate in accordance with the service environment such as load and ambient temperatures.
2. Description of the Prior Art
An increasing number of cooling units using vibrating compressors have been installed on automobiles. In the cooling unit, the d-c power of an automobile, that is, a car battery, is used as the drive source of the vibrating compressor. The vibrating compressor has such a construction that a drive coil caused to vibrate in a magnetic field by an alternating current fed from the outside drives the piston.
In a conventional type of power supply for vibrating compressors using a car battery, for example, as the drive source, where the mechanical resonance frequency of a vibrating compressor is predetermined by its construction, an a-c voltage of a fixed frequency is generated on the basis of the battery voltage end fed to the vibrating compressor.
Since the resonance frequency of the vibrating compressor, however, varies with changes in load, or the service environment, the conventional construction where the power frequency to be fed to the vibrating compressor is kept constant tends to result in poor efficiency.
A control method with good efficiency is desired particularly for applications where a battery is used as the drive source.
The present applicant filed a patent application (Japanese Published Unexamined Patent Application No. Sho-61(1986)-173676) where the vibrating compressor is driven by always keeping it under the optimum condition by causing the vibrating period of the electrical vibrating system in the vibrating compressor to agree with the natural vibrating period of the mechanical vibrating system.
It was experimentally revealed that efficient driving is realized when the difference in first and second peaks of the input current waveform is a certain value.